The invention described herein relates broadly to tough, impact-resistant plastics containing elastomeric polyesters and/or polyurethanes of castor oil. The present invention relates specifically to a process adapted to produce a castor oil-based reinforced product much superior to any heretofore available.
From earlier publications emanating from the laboratory of the inventors herein, it is known that castor oil polyesters or polyurethanes may be used in place of conventional rubbers, such as polybutadiene, as the reinforcement component in impact-resistant or reinforced vinyl plastics, such as polystyrene. These publications are typified by:
G. M. Yenwo, J. A. Manson, J. Pulido, L. H. Sperling, A. Conde, and N. Devia, J. Appl. Polym. Sci., 21, 1531 (1977). PA1 N. Devia-Manjarres, J. A. Manson, L. H. Sperling, and A. Conde, Polym. Eng. Sci., 18, 200 (1978). PA1 G. E. Molau and H. Keskkula, J. Polym. Sci., A-1, 4, 1595 (1966). PA1 C. B. Bucknall, "Toughened Plastics", Applied Science Publishers, Ltd., London, 1977.
These publications suggest both castor oil polyesters or polyurethanes as the reinforcement rubber component in impact-resistant polyvinyl such as polystyrene (when the castor oil elastomer comprises less than about 15% of the mixture) and polyvinyl reinforced castor oil polyurethane or polyester elastomers when the castor oil elastomer comprises more than about 15%.
Inasmuch as a product of the present invention involves simultaneously formed interpenetrating polymer networks, it may be relevant to consider that such polymeric mixtures are in some respects related to graft copolymers. In the graft copolymer art, a number of patents describe systems wherein some form of, at least partially, interpenetrating network of polymers result. Such descriptions are found, for example, in the following patents:
______________________________________ U.S. Patents Foreign Patents ______________________________________ 3,041,292 Br. 1,197,794 3,055,859 Br. 1,239,701 3,316,324 3,426,102 Gr. 2,153,987 3,657,379 Gr. 2,518,904 3,833,404 3,948,823 ______________________________________
It will be noted that none of these patents disclose any relationship of the systems there involved to castor oil based reinforced polyvinyl plastics.
Of further interest, by way of a description of background technology with respect to the present invention, it is reasonably well-known that in the forming of elastomeric reinforced polyvinyl plastic products, it is highly desirable to produce an optimum product by initiating the polymerization of the vinyl component in the mixture to the point of phase separation and then phase inversion (produced upon continued polymerization of the vinyl component and continued stirring, followed by casting or forming of the product and then completion of polymerization of both the vinyl phase and the reinforcement). Such processing conditions are described in the following publications:
That such phase inversion is important to the characteristics of these final products has been known for some time, as shown, for example, by the publications and photomicrographs of Matsuo. (M. Matsuo, Japan Plastics, 2, 6 (July, 1968). (M. Matsuo, Polym. Eng. Sci., 9, 206 (1969).
Notwithstanding the foregoing, there remained a need, prior to the present invention, for tougher and more wear-resistant castor oil elastomer-reinforced polyvinyl compositions. The object of the present invention is to produce such compositions and to provide the process conditions by which such compositions are produced.
With the present invention, this objective is achieved, in part due to the simultaneously formed interpenetrating polymer network of the product. At the same time, the present invention is considered particularly advantageous in its use of castor oil and related products in place of diene and vinyl petroleum-based elastomers as reinforcements in polyvinyl plastics. Castor oil, of course, is a "renewable resource" in that both castor oil and sebacic acid (reactable together to form a castor oil polyester as used in the present invention) are derived from castor beans which are grown in great quantities in many parts of the world, such as India and Brazil. In addition, in the compositions of the present invention, properties comparable or superior to those of petroleum-based reinforced products are obtainable.